Field
This disclosure relates to data processing and compression of raw color-filter array (CFA) sensor data from a digital camera or digital motion picture camera, and more particularly relates to the mathematically lossless image compression of raw CFA data using spatial-domain, rather than frequency-domain, processing methods.
Description of the Background
With the progression of time, the quality of digital cameras has improved, resulting in digital cameras producing higher quality, more detailed images. Digital cameras use charge-coupled device (CCD) or complementary metal-oxide-semiconductors (CMOS) sensors to capture image information as a series of digital values for each point or pixel. The image quality is limited, among other things, by the number of pixels (resolution) and the number of bits per color value (dynamic range). As the number of pixels has increased to produce higher resolutions, and as the bit-depth per pixel has grown, the amount of data per image has increased dramatically.
An image with 2,048 by 1,080 pixels (2K DCI) has 2.2 megapixels. A doubling of the resolution to 4,096 by 2,160 pixels (4K DCI), or 8.8 megapixels, quadruples the amount of data. Along with the increase in the number of pixels, the technology has also progressed to increase the detailed color values with more bits per pixel, called bit-depth. For example, a sensor that has a bit-depth of 8 can produce 256 color values per pixel, whereas a 12-bit sensor produces 4,096 color values per pixel.
The increase in resolution of digital cameras has thus produced more data per image, posing a challenge for the recording of each image. For example, a 10-bit HD (about 2 megapixels) sensor in three colors produces about 66 million bits, or 8.3 megabytes. More recent 4K (8.4 megapixel) digital motion picture cameras with a bit-depth of 16 produce images files with 50.3 megabytes. Since the sensor technology continues to advance, cameras are creating ever-larger data files per image. These large data files create challenges for storing the images, for moving images off a camera, for transferring into or between storage systems, and for transmission to the cloud, and for collaborating in a dispersed geographical workforce.